1. Field of the Invention
This invention relates to a method for modifying the activity and shape selectivity of natural ferrierite so that hydrocarbons are cracked selectively. In particular, it is concerned with a method for making a shape-selective hydrocracking catalyst from natural ferrierite, and with a process for upgrading certain hydrocarbons by shape-selectively cracking the paraffins contained therein. The process may be used to increase the octane number of reformate, or to dewax a waxy-hydrocarbon to reduce its pour point.
2. Description of the Prior Art
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversions. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction. Within these crystals there are numerous small cavities which are interconnected by a number of still smaller channels or pores. These cavities and pores are precisely uniform in size and placement within a specific zeolitic material. Since the dimensions of these pores are such as to accept for absorption only molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and may be utilized to take advantage of this property.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline aluminosilicates. These aluminosilicates can be described as rigid three-dimensional frameworks of SiO.sub.4 and AlO.sub.4 tetrahedra that are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing trivalent aluminum is balanced by the inclusion in the crystal of a cation such as an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of aluminum to the number of various cations, such as Ca/2, Sr/2, Na, K or Li is equal to unity. One type of cation may be exchanged either entirely or partially by another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given aluminosilicate by suitable selection of the cation. The cavities and channels of the crystal are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic aluminosilicates. These aluminosilicates have come to be designated by letter or other convenient symbols, examples of which are zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886), zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No. 3,832,449), zeolite ZSM-23 (U.S. Pat. No. 4,076,842), zeolite ZSM-35 (U.S. Pat. No. 4,016,245) and zeolite ZSM-38 (U.S. Pat. No. 4,046,859).
It is well known in the prior art that certain zeolites such as zeolites A, X, or Y and the naturally occurring zeolites chabazite, erionite, faujasite and mordenite can be stability-enhanced by methods comprising ion exchange and/or heating. U.S. Pat. Nos. 3,354,077; 3,375,065; and 3,402,996 describe such methods. U.S. Pat Nos. 3,997,474 and 4,054,511 to Miale et al, on the other hand, describe a method for activating naturally occurring ferrierite to make it selective primarily for cracking normal paraffins by treatment with ammonium ions and HF. The preparation and use of synthetic ferrierite to increase the octane number of reformates is described by Gianetti et al in Ind. Eng. Chem., Process Design Dev., Vol. 14, No. 1, 1975, pp. 86-92, the entire content of which, including literature cited, is incorporated herein by reference. Also incorporated by reference is Re. 28,398 to Chen et al which describes shape-selective dewaxing with zeolite catalysts.